In a related video, the Brexit designation competition is explainedIBTimes UK

A Brexit campaign has been branded "shameful and cowardly" after it published a poster referencing the Orlando shooting, which left at least 50 people dead at a Florida LGBT nightclub. US national Omar Mateen, 29, was named as the shooter behind the massacre. The security guard reportedly pledged allegiance to the self-styled Islamic State (Isis) terror group during the attack.

"Islamist extremism is a real threat to our way of life. Act now before we see an Orlando-style atrocity here before too long," the Leave.EU poster said. The publication was almost immediately condemned by a number of politicians, including the Education Secretary Nicky Morgan and Labour's Jonathan Ashworth MP.

Hilary Benn, Labour's shadow foreign secretary, issued a statement in response to the poster. "This is a shameful and cowardly poster," he declared.

"It takes courage to stand by your principles and your friends when they are attacked, whether in Orlando, Paris or Brussels. Doing so makes us stronger and shows our resolve to stand up for our values and our way of life in the face of those who hold both in such murderous contempt."

The row comes with 10 days to go until the 23 June referendum, with the latest online opinion poll from YouGov, of more than 1,600 people between 9 and 10 June, putting Leave on 43% and Remain on 42%, while 11% of respondents were undecided.

Leave.EU, co-founded by Ukip donor Arron Banks, lost the official Brexit campaign designation to Vote Leave, which is ran by lobbyist Matthew Elliot and one of Michael Gove's former special advisers, Dominic Cummings. Leave.EU had not responded to a request for comment at the time of publication.